TC 9-62
as well. The magnifier does not change the object that is being magnified; it is only the
image that is larger, not the object itself. With the amplifier, the output signal differs in
amplitude from the input signal, but the input signal still exists unchanged. So, the object
(input signal) and the magnifier (amplifier) control the image (output signal).
5-5.
An amplifier can be defined as a device that enables an input signal to control an
output signal. The output signal will have some (or all) of the characteristics of the input
signal but will generally be larger than the input signal in terms of voltage, current, or
power.
USES OF AMPLIFICATION
5-6.
Most electronic devices use amplifiers to provide various amounts of signal
amplification. Since most signals are originally too small to control or drive the desired
device, some amplification is needed.
5-7.
Figure 5-1 shows an example of the use of an amplifier. In a radio receiver, the
signal picked up by the antenna is too weak (small) to be used as it is, so amplification is
needed. This signal must be amplified before it is sent to the detector. Each time the signal
is amplified it is said to go through a stage of amplification. The detector separates the
audio signal from the frequency that was sent by the transmitter. The audio signal from the
detector will then be amplified to make it large enough to drive the speaker of the radio.
Almost every electronic device contains at least one stage of amplification, so you will be
seeing amplifiers in many devices that you work on.
Figure 5-1. Amplifiers as Used in Radio Receiver
CLASSIFICATION OF AMPLIFIERS
5-8.
Most electronic devices use at least one amplifier. However, there are many types
of amplifiers. It would be impossible to try to describe all the different types of amplifiers.
You will be shown the general principles of amplifiers and some typical amplifier circuits.
5-9.
Most amplifiers can be classified in two ways. The first classification is by their
function. This means they are basically voltage amplifiers or power amplifiers. The second
5-2
TC 9-62
23 June 2005
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